Grease composition, method for evaluating torque performance of grease composition, and method for improving torque performance of grease composition

Abstract

To provide a low-torque grease composition, a method for evaluating the torque performance of the grease composition, and a method for improving the torque performance of the grease composition.SOLUTION: A grease composition comprising a base oil (A) and a thickener (B), wherein when fluorescent pigments having a mean particle size D50 of 3.5 μm or more and 4.5 μm or less are added to the grease composition, fluidity analysis is performed using ParticleImageVelocimetry in a ball-on-disk type device, and the speed of the fluorescent pigments is measured under the following conditions, the speed of the fluorescent pigments is 10mm / s or less. [Measuring Conditions] Speed measuring position: position within 1. 5mm to the left and right from the center of the 1mm in front of the contact portion between the ball and the disk, respectively, position showing maximum speed Number of revolutions of disk: 50 revolutions Applied load: 50N Circumferential speed of disk: 200mm / s Hertz maximum surface pressure between ball and disk: 1. 2GPa SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a grease composition, a method for evaluating the torque performance of a grease composition, and a method for improving the torque performance of a grease composition. [Background technology]

[0002] Grease is a semi-solid lubricant made by dispersing a highly lipophilic solid thickener in a base oil. Grease adheres more easily to the lubricated parts and is less likely to leak out than lubricating oil. Therefore, using grease can simplify the mechanical structure of the lubrication system. Furthermore, grease leaks less than lubricating oil, creating a cleaner environment, and replenishment intervals can be shortened compared to lubricating oil. Grease is mainly used to lubricate machine elements such as rolling bearings, plain bearings, ball screws, linear guides, and gears. Rolling bearings are widely used in machine tool spindles, railroad car carriages, engine accessories such as automobile alternators, constant velocity joints, and wheels.

[0003] Various studies have been conducted to reduce the torque of rolling bearings filled with grease. For example, Patent Document 1 discloses a grease composition containing a base oil and a thickener, in which a flow analysis using Particle Image Velocimetry shows that the proportion of tracer particles having a velocity of 1.0 mm / s or more is 5.0% or more, and the tracer particles are fluorescent pigments with an average particle size of 3.5 μm to 4.5 μm as measured by laser diffraction / scattering. It is disclosed that the grease composition can provide a grease composition that can improve torque performance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-072924 Summary of the Invention [Problem to be solved by the invention]

[0005] In the fluidity analysis using Particle Image Velocimetry described in Patent Document 1, the position where the high-speed camera takes images is 180° from the contact position between the ball and the disc. However, while the 180° position provides insight into the formation of bands and the movement of grease immediately after the ball passes, unless the image is taken at a 0° position, it is not possible to obtain insight into the distribution and flow of grease that contributes to lubrication at the contact point and ultimately torque. Furthermore, it is not easy to estimate how grease flows around the contact point from the results at the 180° position.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a low-torque grease composition, a method for evaluating the torque performance of a grease composition, and a method for improving the torque performance of a grease composition. [Means for solving the problem]

[0007] The present inventors have conducted extensive research into fluidity analysis using Particle Image Velocimetry. As a result, they have found that the behavior of grease at the 0° position can be observed by using a specific filter. They have also found that torque performance can be improved by preparing a grease composition so that the velocity of the fluorescent pigment at the 0° position is equal to or less than a specific value, which led to the completion of the present invention. Specifically, the present invention employs the following configuration. [1] A grease composition containing a base oil (A) and a thickener (B), A grease composition wherein a fluorescent pigment having an average particle diameter D50 of 3.5 μm or more and 4.5 μm or less is added to the grease composition, and when flowability analysis is performed using Particle Image Velocimetry with a ball-on-disk device and the velocity of the fluorescent pigment is measured under the following conditions, the velocity of the fluorescent pigment is 10 mm / s or less. [Measurement conditions] Speed ​​measurement position: The position showing the maximum speed within 1.5 mm on either side of the center, 1 mm in front of the contact point between the ball and the disc. Number of disc revolutions: 50 revolutions Load: 50N Ball and disc peripheral speed: 200 mm / s Maximum Hertzian contact pressure between ball and disc: 1.2 GPa [2] The grease composition according to [1], wherein the thickener (B) includes a urea-based thickener. [3] The grease composition according to [2], wherein the urea-based thickener is a diurea compound obtained by reacting a diisocyanate with a monoamine.

[0008] [4] A method for evaluating the torque performance of a grease composition, comprising the steps of adding a fluorescent pigment having an average particle diameter D50 of 3.5 μm or more and 4.5 μm or less to the grease composition, performing a flowability analysis using Particle Image Velocimetry in a ball-on-disk type device, and measuring the velocity of the fluorescent pigment under the following conditions: [Measurement conditions] Speed ​​measurement position: The position showing the maximum speed within 1.5 mm on either side of the center, 1 mm in front of the contact point between the ball and the disc. Number of disc revolutions: 50 revolutions Load: 50N Ball and disc peripheral speed: 200 mm / s Maximum Hertzian contact pressure between ball and disc: 1.2 GPa

[0009] [5] A method for improving torque performance of a grease composition, comprising: a method for improving the torque performance of a grease composition, the method comprising the steps of: adding a fluorescent pigment having an average particle diameter D50 of 3.5 μm or more and 4.5 μm or less to the grease composition; performing a flowability analysis using Particle Image Velocimetry with a ball-on-disk device; and adjusting the velocity of the fluorescent pigment so that the velocity is 10 mm / s or less when measured under the following conditions: [Measurement conditions] Speed ​​measurement position: The position showing the maximum speed within 1.5 mm on either side of the center, 1 mm in front of the contact point between the ball and the disc. Number of disc revolutions: 50 revolutions Load: 50N Ball and disc peripheral speed: 200 mm / s Maximum Hertzian contact pressure between ball and disc: 1.2 GPa [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a low-torque grease composition, a method for evaluating the torque performance of a grease composition, and a method for improving the torque performance of a grease composition. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 shows a schematic of a ball-on-disk experimental setup that can be used as a measuring device for fluorescent pigment velocities. [Figure 2] FIG. 1 shows the flow velocity distribution and measurement positions of a fluorescent pigment in a flow analysis using Particle Image Velocimetry. [Figure 3] 1 is a graph showing the results of flowability analysis of the grease composition of Comparative Example 1 using Particle Image Velocimetry. [Figure 4] 1 is a graph showing the results of flowability analysis of the grease composition of Example 1 using Particle Image Velocimetry. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Grease composition) The grease composition of the present embodiment contains a base oil (A) and a thickener (B). In the grease composition of this embodiment, a fluorescent pigment having an average particle diameter D50 of 3.5 μm or more and 4.5 μm or less is added to the grease composition of this embodiment, and when a flowability analysis is performed using Particle Image Velocimetry with a ball-on-disk type device and the speed of the fluorescent pigment is measured under the following conditions, the speed of the fluorescent pigment is 10 mm / s or less. [Measurement conditions] Speed ​​measurement position: The position showing the maximum speed within 1.5 mm on either side of the center, 1 mm in front of the contact point between the ball and the disc. Number of disc revolutions: 50 revolutions Load: 50N Ball and disc peripheral speed: 200 mm / s Maximum Hertzian contact pressure between ball and disc: 1.2 GPa

[0013] The fluorescent pigment used in this measurement has an average particle size D50 of 3.5 μm or more and 4.5 μm or less. A specific example is FA-207LF manufactured by Shin-Roi-Hi Co., Ltd. The average particle diameter D50 can be determined from the particle size distribution of the fluorescent pigment measured by a laser diffraction scattering method.

[0014] Particle Image Velocimetry (hereinafter referred to as "PIV") using a ball-on-disk type device is a fluid visualization technique that measures direction and velocity by irradiating fluorescent pigments in space with laser light twice in succession and analyzing the brightness distribution of the fluorescent pigments in two consecutive images of the fluorescent pigments taken at the same time as the irradiation. That is, the velocity of the fluorescent pigment means the speed at which the fluorescent pigment contained in the grease composition moves in any direction.

[0015] The high velocity of the fluorescent pigment in the grease composition at the contact area between the ball and the disc means that the flow of the grease composition inside the bearing is not impeded. Therefore, it is presumed that the high velocity of the fluorescent pigment in the grease composition at the contact point between the ball and the disk reduces the torque of the rolling bearing because the ball inside the bearing does not encounter resistance when passing over the transfer surface. On the other hand, the fact that the fluorescent pigment velocity is high at "positions showing maximum velocity within 1.5 mm on either side of the center, 1 mm in front of the contact point between the ball and disc" suggests that the grease composition is in a state of greater fluidity due to shear between the ball and disc. Therefore, the fact that the speed of the fluorescent pigment is high at "the position showing the maximum speed within 1.5 mm on either side of the center, 1 mm in front of the contact point between the ball and the disc" suggests that the torque of the rolling bearing increases because of the increased resistance caused by the flow of grease when the ball inside the bearing passes over the transfer surface. In view of the above, the grease composition of this embodiment is preferably a grease composition that causes the fluorescent pigment to move at a speed of 10 mm / s or less, more preferably a grease composition that causes the fluorescent pigment to move at a speed of 8 mm / s or less, and even more preferably a grease composition that causes the fluorescent pigment to move at a speed of 5 mm / s or less.

[0016] The speed of the fluorescent pigment is measured under the conditions described above, and the diameter of the disk and the materials of the ball and disk can be appropriately selected or adjusted so that the peripheral speed of the disk is 200 mm / s and the maximum Hertzian surface pressure is 1.2 GPa. For example, the disk may be made of sapphire glass. For example, the size of the disk may be 105 mm in diameter and 12 mm in thickness. For example, the material of the balls may be SUJ2 (high carbon chromium bearing steel). For example, the diameter of the ball is 20 mm or more and 22 mm or less, and is preferably 22 mm.

[0017] A ball-on-disk type experimental device, as shown in Figure 1, can be used to measure the velocity of the fluorescent pigment. A grease composition containing dispersed fluorescent pigment for PIV is applied to the disk, and the velocity of the fluorescent pigment is analyzed after the ball and disk are rotated. A ball-on-disk type experimental apparatus such as that shown in Figure 1 can be designed by a person skilled in the field of lubricants. The configuration of the experimental apparatus is similar to that used for measuring the thickness of an oil film made from grease or lubricating oil, and a person skilled in the field of lubricants can make the necessary modifications and use it to measure the velocity of fluorescent pigments. The configuration of an experimental apparatus used for measuring the thickness of an oil film made from grease or lubricating oil is exemplified, for example, in the following documents:

[0018] Measurement of Nanometer-Scale Oil Film Thickness and Wear in Pure Sliding Contact by Ultrathin Film Optical Interferometry, Journal of Japanese Society of Tribologists, Vol. 52, No. 11, pp. 818-826, Published: November 15, 2007 ·Effects of a thickener structure on grease elastohydrodynamic lubrication films, Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology Volume:214 Issue:4,page(s):327-336

[0019] An example of a procedure for determining the velocity of a fluorescent pigment in a grease composition is described below. A fluorescent pigment is added to a grease composition, and the composition is applied to the surface of a disc in a ball-on-disc experimental device. The thickness of the applied grease composition can be adjusted appropriately depending on the consistency of the grease composition and the measurement conditions for the speed of the tracer particles, but it is preferably 5 μm or more and 15 μm or less (e.g., 10 μm). Thereafter, the grease composition applied to the surface of the disc is brought into contact with a ball, and a load is applied. Next, the ball and disc are driven, and the sliding surface of the disc (trajectory mark) immediately after the ball passes through is photographed with a high-speed camera. Figure 2 shows the flow velocity distribution and measurement positions of fluorescent pigment in a fluidity analysis using Particle Image Velocimetry. Although it is difficult to judge the flow velocity of fluorescent pigment from the color, it is actually possible to judge the flow velocity from the color. In the image taken with the high-speed camera in Figure 2, point A is the contact point between the ball and the disc. Point B0 is a point 1 mm in front of the contact point between the ball and the disc. Points B1 and B2 are points located 1.5 mm to the left and right of the contact point. The flow velocity of the fluorescent pigment on the line connecting points B1 and B2 is measured, and the maximum velocity is detected.

[0020] In this measurement, since the measurement position is near the contact point between the ball and the disc, a filter must be used to detect only the excitation wavelength of the fluorescent pigment without detecting the reflected laser light. One example of such a filter is the YA3 Professional monochrome contrast filter manufactured by Kenko Tokina Corporation.

[0021] When the grease composition of this embodiment is subjected to the above-mentioned PIV flow analysis and the speed of the fluorescent pigment is measured, the speed of the fluorescent pigment can be controlled to be 10 mm / s or less by adjusting the combination and contents of the base oil (A) and the thickener (B), and by performing homogenization by a three-roll mill treatment for a long period of time in the production process of the grease composition of this embodiment.

[0022] <Base oil (A)> The grease composition of the present embodiment contains a base oil (A). The base oil (A) may be a mineral oil or a synthetic oil.

[0023] <Mineral oil> Mineral oils can be distillates obtained by atmospheric distillation of crude oil. Lubricating oil fractions obtained by further vacuum distillation of the distillates and then refining them through various refining processes can also be used. Refining processes can include hydrorefining, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, and clay treatment, and can be combined as appropriate. Mineral oils can be obtained by combining these refining processes in an appropriate order. Mixtures of refined oils with different properties, obtained by subjecting different crude oils or distillates to a combination of different refining processes, can also be used.

[0024] ≪Synthetic oil≫ Examples of synthetic oils include polyolefins such as poly-α-olefins, ester base oils such as diesters and polyol esters, polyalkylene glycols, alkylbenzenes, alkylnaphthalenes, and GTL base oils. Among the synthetic oils, poly-α-olefins are preferred in terms of availability, cost, viscosity characteristics, and oxidation stability.

[0025] Among the above, the base oil (A) preferably contains a synthetic oil, and more preferably contains a poly-α-olefin.

[0026] The grease composition of this embodiment can use mineral oils or synthetic base oils either alone or in combination of two or more.

[0027] The kinematic viscosity of the base oil at 40°C is preferably 15mm 2 / s or more, preferably 30 mm 2 / s or more, preferably 100 mm 2 / s or less, preferably 70 mm 2 In one embodiment, the kinematic viscosity of the base oil at 40°C is preferably 15 mm / s or less.2 / s or more 100mm 2 / s or less, preferably 30 mm 2 / s or more 70mm 2 / s or less. In this specification, the kinematic viscosity at 40°C means the kinematic viscosity at 40°C measured in accordance with JIS K2283:2000.

[0028] The content of the base oil is preferably 60% by mass or more, more preferably 70% by mass or more, and is preferably 97% by mass or less, more preferably 95% by mass or less, based on the total amount of the grease composition. In one embodiment, the content of the base oil is preferably 60% by mass or more and 97% by mass or less, and more preferably 70% by mass or more and 95% by mass or less. When the content of the base oil is within the above-mentioned preferred range, it becomes easier to obtain a grease composition that satisfies the above-mentioned parameters.

[0029] <Thickener (B)> The grease composition of the present embodiment contains a thickener (B). As the thickener (B), metal soap-based thickeners and urea-based thickeners are preferred.

[0030] <Metal soap-based thickener> Metal soap thickeners include simple soaps and complex soaps. Simple soaps are metal soaps in which fatty acids or fats are saponified with alkali metal hydroxides or alkaline earth metal hydroxides. Complex soaps are complexes in which an organic acid with a different molecular structure is combined with the fatty acid used in simple soaps. The fatty acid may be a fatty acid derivative having a hydroxy group or the like. As the fatty acid, monovalent or divalent aliphatic carboxylic acids are preferred. As the fatty acid, aliphatic carboxylic acids having 6 to 20 carbon atoms are preferred, and monovalent aliphatic carboxylic acids having 12 to 20 carbon atoms or divalent aliphatic carboxylic acids having 6 to 14 carbon atoms are more preferred. As the fatty acid, monovalent aliphatic carboxylic acids having one hydroxy group are preferred. As the organic acid to be combined with the fatty acid in complex soaps, dibasic acids such as acetic acid, azelaic acid, or sebacic acid, or benzoic acid are preferred. The metal for the metal soap thickener may be an alkali metal such as lithium or sodium, an alkaline earth metal such as calcium, or an amphoteric metal such as aluminum. In the present invention, "having 6 to 20 carbon atoms" means having 6 or more and 20 or less carbon atoms.

[0031] <Urea-based thickener> As the urea-based thickener, for example, a diurea compound obtained by the reaction of a diisocyanate with a monoamine, or a polyurea compound obtained by the reaction of a diisocyanate with a monoamine or diamine can be used.

[0032] Diisocyanates are compounds in which two hydrogen atoms of a hydrocarbon are substituted with isocyanate groups. The hydrocarbon may be an acyclic hydrocarbon or a cyclic hydrocarbon, and may be any of an aromatic hydrocarbon, an alicyclic hydrocarbon, or an aliphatic hydrocarbon. The number of carbon atoms in these hydrocarbons is preferably 4 to 20, more preferably 8 to 18. Preferred specific examples of diisocyanates include phenylene diisocyanate, tolylene diisocyanate, biphenyl diisocyanate (diphenyl diisocyanate), diphenylmethane diisocyanate, octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate. One type of diisocyanate may be used alone, or two or more types may be used in combination.

[0033] A monoamine is a compound having one amino group per molecule. Preferred monoamines include octylamine, dodecylamine, hexadecylamine, stearylamine (octadecylamine), oleylamine, aniline, p-toluidine, and cyclohexylamine. A diamine is a compound having two amino groups per molecule. Preferred diamines include ethylenediamine, propanediamine, butanediamine, hexanediamine, octanediamine, phenylenediamine, tolylenediamine, xylenediamine, and diaminodiphenylmethane. The hydrocarbon group of the monoamine or diamine may be an acyclic hydrocarbon group or a cyclic hydrocarbon group, or may be an aromatic hydrocarbon group, an alicyclic hydrocarbon group, or an aliphatic hydrocarbon group. The number of carbon atoms is preferably 2 to 20, more preferably 4 to 18, even more preferably 4 to 10, particularly preferably 6 to 8, and most preferably 8.

[0034] The urea thickener is preferably a diurea compound obtained by reacting a diisocyanate with a monoamine. The monoamine is preferably a monoamine having 2 to 20 carbon atoms, more preferably a monoamine having 4 to 18 carbon atoms, even more preferably a monoamine having 4 to 10 carbon atoms, particularly preferably a monoamine having 6 to 8 carbon atoms, and most preferably a monoamine having 8 carbon atoms. Specifically, cyclohexylamine, octylamine, and stearylamine are preferred, cyclohexylamine and octylamine are more preferred, and octylamine is even more preferred.

[0035] The thickener (B) may be used alone or in combination of two or more kinds. The content of the thickener (B) is preferably 2% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, relative to the total amount of the grease composition of this embodiment, and is preferably 30% by mass or less, and more preferably 20% by mass or less. In one embodiment, the content of the thickener (B) is preferably 2% by mass or more and 40% by mass or less, more preferably 3% by mass or more and 40% by mass or less, and even more preferably 5% by mass or more and 30% by mass or less.

[0036] <Optional ingredients> The grease composition of this embodiment may contain optional components other than the base oil (A) and thickener (B), such as solid lubricants, antiwear or extreme pressure agents, antioxidants, oiliness agents, rust inhibitors, and corrosion inhibitors.

[0037] Examples of solid lubricants include graphite, graphite fluoride, melamine cyanurate, polytetrafluoroethylene, molybdenum disulfide, antimony sulfide, boron nitride, and alkaline (earth) metal borates. When the grease composition contains a solid lubricant, the content thereof is, for example, 0.1 to 20 mass% relative to the total amount of the grease composition. One type of solid lubricant may be used alone, or multiple solid lubricants may be used in combination.

[0038] Examples of anti-wear agents or extreme pressure agents include organic zinc compounds such as zinc dialkyldithiophosphate and zinc dialkyldithiocarbamate; sulfur-containing compounds such as molybdenum dialkyldithiocarbamate, dihydrocarbyl polysulfide, sulfurized esters, thiazole compounds, and thiadiazole compounds; and phosphorus-based extreme pressure agents such as phosphate esters, acid phosphate esters, amine salts of acid phosphate esters, and phosphites. When the grease composition contains an anti-wear agent or extreme pressure agent, the content thereof is, for example, 0.1 to 10 mass% based on the total amount of the grease composition. One type of anti-wear agent or extreme pressure agent may be used alone, or multiple anti-wear agents or extreme pressure agents may be used in combination.

[0039] Examples of antioxidants include phenolic compounds such as 2,6-di-t-butylphenol and 2,6-di-t-butyl-p-cresol; and amine compounds such as diphenylamine, dialkyldiphenylamine, phenyl-α-naphthylamine, and p-alkylphenyl-α-naphthylamine. When the grease composition contains an antioxidant, the content thereof is, for example, 0.5 to 10 mass% relative to the total amount of the grease composition. One type of antioxidant may be used alone, or multiple antioxidants may be used in combination.

[0040] Examples of oily agents include amines such as laurylamine, myristylamine, palmitylamine, stearylamine, and oleylamine; higher alcohols such as lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, and oleyl alcohol; higher fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid; fatty acid esters such as methyl laurate, methyl myristate, methyl palmitate, methyl stearate, and methyl oleate; and fats and oils such as glycerin oleate and glycerin stearate. When the grease composition contains an oily agent, the content thereof is, for example, 0.01 to 5% by mass relative to the total amount of the grease composition. One oily agent may be used alone, or multiple oily agents may be used in combination.

[0041] Examples of rust inhibitors include amines, neutral or overbased petroleum-based or synthetic oil-based metal sulfonates, metal carboxylates, esters, phosphoric acid, phosphates, etc. When the grease composition contains a rust inhibitor, the content thereof is, for example, 0.005 to 5 mass% relative to the total amount of the grease composition. One type of rust inhibitor may be used alone, or multiple rust inhibitors may be used in combination.

[0042] As the corrosion inhibitor, for example, known corrosion inhibitors such as benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, and imidazole-based compounds can be used. When the grease composition contains a corrosion inhibitor, the content thereof is, for example, 0.01 to 10 mass% relative to the total amount of the grease composition. The corrosion inhibitor may be used alone, or multiple corrosion inhibitors may be used in combination.

[0043] (Method for evaluating the fluidity of a grease composition) The method for evaluating the fluidity of a grease composition of this embodiment includes the steps of adding a fluorescent pigment having an average particle diameter D50 of 3.5 μm or more and 4.5 μm or less to the grease composition, performing a fluidity analysis using Particle Image Velocimetry in a ball-on-disk device, and measuring the velocity of the fluorescent pigment under the following conditions: [Measurement conditions] Speed ​​measurement position: The position showing the maximum speed within 1.5 mm on either side of the center, 1 mm in front of the contact point between the ball and the disc. Number of disc revolutions: 50 revolutions Load: 50N Ball and disc peripheral speed: 200 mm / s Maximum Hertzian contact pressure between ball and disc: 1.2 GPa

[0044] (Method for evaluating torque performance of grease composition) The method for evaluating the torque performance of the grease composition of this embodiment involves adding a fluorescent pigment having an average particle diameter D50 of 3.5 μm or more and 4.5 μm or less to the grease composition, performing a flowability analysis using Particle Image Velocimetry with a ball-on-disk device, and measuring the speed of the fluorescent pigment under the following conditions. If the speed of the fluorescent pigment is 10 mm / s or less, it can be evaluated that the torque is reduced compared to a grease composition in which the speed of the fluorescent pigment exceeds 10 mm / s. [Measurement conditions] Speed ​​measurement position: The position showing the maximum speed within 1.5 mm on either side of the center, 1 mm in front of the contact point between the ball and the disc. Number of disc revolutions: 50 revolutions Load: 50N Ball and disc peripheral speed: 200 mm / s Maximum Hertzian contact pressure between ball and disc: 1.2 GPa

[0045] Specific methods for preparing the grease composition include adjusting the combination and contents of the base oil (A) and the thickener (B), and adjusting the processing time of the three-roll mill treatment in the production process of the grease composition. [Example]

[0046] The present invention will be described below using examples that are embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0047] <Formulation of grease composition> The grease compositions of Example 1 and Comparative Examples 1 and 2 were prepared by blending the base oil (A) and the thickener (B) by the following method in the blending ratios shown in Table 1. The values ​​in Table 1 indicate the content (mass%) relative to the total amount of the grease composition. · Mixing process The resulting semi-solid composition was kneaded twice using a non-hydraulic three-roll mill under the following manufacturing conditions to prepare the grease compositions of each example. ≪Manufacturing conditions≫ Shear rate: 1.4 x 10 between the first and second rolls 3 / s, 1.2 × 10 between the second and third rolls 4 / s Distance between rolls: 0.15 mm between the first and second rolls, 0.05 mm between the second and third rolls

[0048] (1) Base oil (A) Base oil (A)-1: Poly-α-olefin (40°C kinematic viscosity = 47.5 mm 2 / s)

[0049] (2) Thickener (B) (B)-1: Urea thickener (a diurea compound obtained by the reaction of octylamine with diisocyanate) (b)-1: Urea thickener (a diurea compound obtained by the reaction of cyclohexylamine with diisocyanate) (b)-2: Urea thickener (a diurea compound obtained by the reaction of octadecylamine with diisocyanate)

[0050] [Consistency evaluation] The worked penetration of each grease composition measured in accordance with JIS K2220:2013 is shown in Table 1.

[0051] [Evaluation of the speed of fluorescent pigments] A fluorescent pigment (FA-207LF manufactured by Shin-Roi-Hi Co., Ltd.) with an average particle diameter D50 of 3.5 μm or more and 4.5 μm or less was added to each grease composition, and flowability analysis was performed using Particle Image Velocimetry with a ball-on-disk device to measure the velocity of the fluorescent pigment under the following conditions. Figure 3 shows the measurement results of the fluorescent pigment velocity in the grease composition of Comparative Example 1. Figure 4 shows the measurement results of the fluorescent pigment velocity in the grease composition of Example 1. [Measurement conditions] Velocity measurement location: 1 mm to the left and right of the center of the contact point between the ball and the disc Number of disc revolutions: 50 revolutions Load: 50N Ball and disc peripheral speed: 200 mm / s Maximum Hertzian contact pressure between ball and disc: 1.2 GPa Disc material: Sapphire glass Disc size: 105mm diameter, 12mm thickness Ball material: SUJ2 (high carbon chromium bearing steel) Ball diameter: 22mm

[0052] [Torque rating] The evaluation was conducted on a deep groove ball bearing with a resin cage and non-contact seal, filled with 0.6 g of the grease product. An axial load of 50 N was applied, and the inner ring was rotated at 200 rpm in a room temperature environment. The tangential force tending to rotate the outer ring was measured with a load cell, and the rotational torque was calculated. The evaluation time was 10 minutes.

[0053] [Table 1]

[0054] As shown in Table 1, the grease composition of Example 1, which is a grease composition in which the speed of the fluorescent pigment is 10 mm / s or less, had low torque.

Claims

1. A grease composition containing a base oil (A) and a thickener (B), A grease composition wherein a fluorescent pigment having an average particle diameter D50 of 3.5 μm or more and 4.5 μm or less is added to the grease composition, and when a flowability analysis is performed using Particle Image Velocimetry in a ball-on-disk type device and the speed of the fluorescent pigment is measured under the following conditions, the speed of the fluorescent pigment is 10 mm / s or less. [Measurement conditions] Velocity measurement position: The position showing the maximum velocity within 1.5 mm on either side of the center, 1 mm in front of the contact point between the ball and the disc. Number of disc revolutions: 50 revolutions Load: 50N Disk peripheral speed: 200 mm / s Maximum Hertzian surface pressure between ball and disc: 1.2 GPa

2. The grease composition according to claim 1 , wherein the thickener (B) includes a urea-based thickener.

3. 3. The grease composition according to claim 2, wherein the urea-based thickener is a diurea compound obtained by reacting a diisocyanate with a monoamine.

4. A method for evaluating the torque performance of a grease composition, comprising the steps of adding a fluorescent pigment having an average particle diameter D50 of 3.5 μm or more and 4.5 μm or less to the grease composition, performing a flowability analysis using Particle Image Velocimetry in a ball-on-disk type device, and measuring the velocity of the fluorescent pigment under the following conditions: [Measurement conditions] Velocity measurement position: The position showing the maximum velocity within 1.5 mm on either side of the center, 1 mm in front of the contact point between the ball and the disc. Number of disc revolutions: 50 revolutions Load: 50N Disk peripheral speed: 200 mm / s Maximum Hertzian surface pressure between ball and disc: 1.2 GPa

5. A method for improving torque performance of a grease composition, comprising: a method for improving the torque performance of a grease composition, the method comprising the steps of: adding a fluorescent pigment having an average particle diameter D50 of 3.5 μm or more and 4.5 μm or less to the grease composition; performing a flowability analysis using Particle Image Velocimetry in a ball-on-disk type device; and adjusting the velocity of the fluorescent pigment to 10 mm / s or less when measured under the following conditions: [Measurement conditions] Velocity measurement position: The position showing the maximum velocity within 1.5 mm on either side of the center, 1 mm in front of the contact point between the ball and the disc. Number of disc revolutions: 50 revolutions Load: 50N Disk peripheral speed: 200 mm / s Maximum Hertzian surface pressure between ball and disc: 1.2 GPa

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